1. Field of the Invention
This invention relates to manufacture of high strength composite structures using layers of initially spunbonded material.
2. Description of the Prior Art
U.S. Pat. No. 4,311,273, issued Jan. 19, 1982 on the application of Ronald P. Marsh, relates to a multi-layer structure of nonwoven sheets wherein adjacent sheets in the structure are joined by means of needle-punching with barbed needles. This reference also discloses needle-punching the individual layers separately in order to increase porosity prior to impregnation with thermosetting resins.
U.S. Pat. No. 3,670,506 issued June 20, 1972 on the application of Yves Gaudard, relates to manufacture of spunbonded structures wherein the exterior surfaces of a thick web of melt spun filaments are calendered hot and then are needle-punched to enmesh the filaments from one surface to the other through the thickness of the structure.